1. Field of the Invention
This invention generally relates to electrochemical cells and, more particularly, to a reactive separator to prevent the formation of metal dendrites in metal-ion batteries.
2. Description of the Related Art
Lithium-ion batteries (LIBs) are widely used in a vast number of applications such as power sources for electronic devices, electric vehicles, and energy storage devices for wind and solar power. However, one of the major safety issues for LIBs is lithium plating and dendrite formation during the charge process. Although graphite is used as a non-lithium-metal anode in state-of-the-art LIBs, lithium plating can still occur when the battery is subjected to abuse such as fast-charging, low-temperature environments, and overcharging.
Lithium plating results in the formation of lithium dendrites that penetrate through the porous separator and short the battery. Serious consequences such as fire and explosions can be caused by such lithium dendrite formation and growth. Dendrite formation is worse when a lithium metal anode is used in the battery. However, the substitution of lithium metal for graphite is desirable in light of the resulting increase in energy density of LIBs and in the development of batteries beyond LIBs, such as lithium-sulfur and lithium-air batteries.
Other alkali and alkaline earth metal-ion batteries, especially the rechargeable sodium-ion battery (SIB), have attracted a lot of research attention because of their low-cost and comparable energy density as compared to LIBs. Unlike LIBs, graphite is incapable of sodium accommodation in a sodium battery. Hard carbon is considered to be the most likely non-sodium-metal anode for SIBS in the foreseeable future. However, the potential for sodium intercalation into hard carbon is mainly below 100 millivolts (mV) and the sodium diffusion is slow between different sites in a hard carbon anode. These characteristics lead to the hazard of sodium dendrites when hard carbon is used in a SIB. Since the ionic radius becomes larger and larger in the elements of lithium to sodium, potassium, and cesium, and since few non-metal anodes have been reported for these metal-ion batteries, it is reasonable to conclude that the dendrite issue will remain as a major obstacle in the development of novel rechargeable metal-ion batteries.
In order to prevent metal dendrite growth/penetration, several strategies have been developed in the past decades. Electrolyte additives are proven to be helpful to form a uniform solid electrolyte interface (SEI) layer on the anode surface, which is beneficial both to suppressing electrolyte decomposition and dendrite growth, but no reported additive can eliminate dendrite growth completely. A dense solid state electrolyte membrane, which can be either ceramic or polymer, is considered to be the most efficient dendrite penetration blocker, but the low conductivity and high fabrication cost of these membranes prevent their large-scale application. Gel-like polymer electrolytes without inorganic fillers have also demonstrated the ability to block dendrite growth at certain level, but the instability of these electrolytes at the anode electrode surface and the unstable structure of the gel-electrolyte remain as unsolved problems for practical applications.
It would be advantageous if a structure existed that would react with lithium, sodium, or any other alkali and alkaline (earth) metal dendrite and therefore protect a battery from an internal short circuit, enabling a battery to achieve ultra-long cycle life with improved safety.